This invention relates to a method of controlling a kiln plant and to a system for implementing the method.
In the manufacturing of cement, a kiln plant is used to convert raw meal to clinker which is then milled together with other materials to produce cement. Due to the large number of variables which affect the operation of the kiln plant and the quality of the clinker, various control systems and methods have been proposed over the years. Nevertheless, it remains difficult to optimise the operation of such a plant, particularly due to variations in the feed material, fuel quality, ambient conditions and other variables.
According to a first aspect of the invention there is provided a controller for a kiln plant, the controller comprising:
a first temperature sensor arranged to measure the temperature at or near the hood of the kiln and to generate an output indicative of this temperature;
gas sensing means arranged to measure the concentration in the kiln of at least one gas from the group comprising O2, NOX, SOX and CO and to generate at least one respective output indicative of the relevant gas concentration; and
control means adapted to receive the output from the first temperature sensor and to control the amount of fuel fed to the firing end of the kiln to maintain the temperature at or near the hood of the kiln within a predetermined range, the control means being further adapted to receive said at least one output from the gas sensing means and to control at least a main impeller of the kiln to maintain the concentration of said at least one gas within a predetermined range.
The controller preferably further comprises a second temperature sensor arranged to measure the temperature at or near the back end of the kiln and to generate an output indicative of this temperature, the control means being further adapted to receive the output from the second temperature sensor and to control the amount of fuel fed to the back end of the kiln to maintain the temperature at or near the back end of the kiln within a predetermined range.
The control means may further include a control matrix which includes values determinative of the relationships between a plurality of plant measurements including the temperature at or near the hood of the kiln, the temperature at or near the back end of the kiln, and O2, NOX, SOX and CO concentrations, and a plurality of operating parameters including the amount of fuel fed to the firing end of the kiln, the amount of fuel fed to the back end of the kiln, the main impeller speed, the kiln speed, the kiln main drive current, the raw meal feed, the cooler air flow and cooler grate speed.
The invention also extends to a method of controlling a kiln plant using the controller described above.
According to a second aspect of the invention there is provided control means for a kiln plant, the control means comprising an outer quality controller cascaded to at least one inner controller, wherein the outer quality controller comprises a first feedback controller being adapted to receive a first setpoint input indicating a desired amount of 3CaO.SiO2 and/or 2CaO.SiO2 and/or another clinker chemical property to be present in clinker produced by the kiln plant, and a second feedback input indicating the actual amount of 3CaO.SiO2 and/or 2CaO.SiO2 and/or another clinker chemical property present in clinker being produced by the kiln plant, the first feedback controller being further adapted to compare the first setpoint input and the second input and, if the inputs differ, to produce an output to alter a setpoint input to the inner controller directly or indirectly to adjust one or more of the kiln plant""s operating parameters so that the amount of 3CaO.SiO2 and/or 2CaO.SiO2 and/or another clinker chemical property in the clinker produced by the kiln plant will be substantially equal to the desired amount of 3CaO.SiO2 and/or 2CaO.SiO2 and/or another clinker chemical property.
Preferably, the inner controller is a free lime controller, wherein the second setpoint input comprises a dynamic setpoint for the free lime content of the clinker to the inner controller, and wherein the inner controller is adapted to receive an input indicating the actual amount of free lime present in clinker being produced by the kiln plant, the inner controller being further adapted to compare the dynamic setpoint for the free lime content and the actual amount of free lime present and, if these differ, to produce an output to directly or indirectly alter one or more of the kiln plant""s operating parameters so that the amount of free lime present in the clinker produced by the kiln plant will be substantially equal to the dynamic setpoint for the free lime content.
In a first embodiment of the second aspect of the invention, the control means may still further include a thermodynamic controller, cascaded to the inner controller, wherein the inner controller outputs a setpoint for at least one plant measurement to the thermodynamic controller, and wherein the thermodynamic controller is adapted to receive an input from the kiln plant indicating the value of the at least one plant measurement, the thermodynamic controller being further adapted to compare the setpoint for the at least one plant measurement and the value of the at least one plant measurement and, if these differ, to produce an output to alter one or more of the kiln plant""s operating parameters.
Preferably, the inner controller is arranged to output a plurality of dynamic setpoints for a plurality of plant measurements to the thermodynamic controller, the plurality of plant measurements constituting controlled variables and being selected from the group including the back end temperature, the hood temperature, the level of CO, the level of NOX, the level of SOX and the level of O2.
The kiln plant""s operating parameters may comprise one or more of the group constituting manipulated variables comprising the total fuel fed to the kiln plant, the percentage fuel fed to the back of the kiln plant or any other derived measurement or indication of the fuel being fed to the plant, the main impeller speed, the kiln speed, the cooler air flow and the cooler grate speed. These parameters are manipulated to alter the plant measurements to approach respective setpoints, using a control matrix which includes values determinative of the relationships between the operating parameters and plant measurements.
In a second embodiment of the second aspect of the invention, the control means may still further include a thermodynamic controller connected to the kiln plant, wherein the thermodynamic controller is adapted to receive an input from the kiln plant indicating the value of at least one plant measurement, the controller being further adapted to compare a setpoint for the at least one plant measurement and the value of the at least one plant measurement and, if these differ, producing an output to alter one or more of the kiln plant""s operating parameters, wherein the at least one of the kiln plant""s operating parameters controlled by the thermodynamic controller is different from the one or more operating parameters controlled by the free lime controller.
The at least one or more of the kiln plant""s operating parameters controlled by the thermodynamic controller comprise at least one of the group comprising the total coal fed to the kiln, the main impeller speed, the kiln speed, the raw meal feed, the cooler air flow and the cooler grate speed and wherein the kiln plant""s operating parameter controlled by the free lime controller is the percentage fuel fed to the back of the kiln.
In a third embodiment of the second aspect of the invention, the inner controller is a thermodynamic controller, wherein the second setpoint input from the outer quality controller to the thermodynamic controller is a setpoint for at least one plant measurement, and wherein the thermodynamic controller is adapted to receive an input from the kiln plant indicating the value of the at least one plant measurement, the thermodynamic controller being further adapted to compare the setpoint for the at least one plant measurement and the input indicating the value of the at least one plant measurement and, if these differ, to produce an output to alter one or more of the kiln plant""s operating parameters.
The at least one plant measurement may be one or more of the plant measurements selected from the group including the back end temperature, the hood temperature and the level of NOX.
Preferably, the at least one plant measurement is the hood temperature.
In this embodiment, the control means also includes a free-lime controller arranged to receive a setpoint input for the free-lime content of the clinker and an input indicating the actual amount of free-lime present in clinker being produced by the kiln plant, the free-lime controller being further adapted to compare the setpoint for the free-lime content and the input indicating the actual amount of free-lime present and, if these differ, to produce an output to directly or indirectly alter one or more of the kiln plant""s operating parameters so that the amount of free-lime present in the clinker produced by the kiln plant will be substantially equal to the setpoint for the free-lime content.
The setpoint for the free-lime may be received from the 3CaO.SiO2 controller, or may be manually inputted by an operator of the controller.
The one or more operating parameters controlled by the free-lime controller are different from the one or more operating parameters controlled by the thermodynamic controller.
Preferably, the operating parameter controlled by the free-lime controller is the percentage fuel fed to the back of the kiln.
The invention also extends to a method of controlling a kiln plant using the controller described above.